Fuel cell stacks and methods

ABSTRACT

The invention provides a fuel cell stack including a layer of encapsulating material disposed about the separator plate, MEA, and reactant manifold, wherein the reactant manifold is bounded at least in part by the encapsulating material. The fuel cell stack also includes a first opening through the plate body to the first face from the second face, and an open channel in the second face extending from the opening toward a periphery of the plate. The invention also provides a fuel cell stack having a first face including an opening for passage of a reactant therethrough, a first reactant flow field defined thereon, and a first raised surface formed thereon substantially surrounding the opening. The first raised surface is configured and adapted to mate with a second surface on a face of an adjacent plate to create a flow obstruction for encapsulating material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel cell stack for generatingelectrical energy. Particularly, the present invention is directed to afuel cell stack including a layer of encapsulating material.

2. Description of Related Art

Membrane based electrochemical cells, and particularly, proton exchangemembrane (PEM) fuel cells are well known. PEM fuel cells convertchemical energy to electrical power with virtually no environmentalemissions and differ from a battery in that energy is not stored, butderived from supplied fuel. Therefore, a fuel cell is not tied to acharge/discharge cycle and can maintain a specific power output as longas fuel is continuously supplied. Significant funds have been investedin fuel cell research and commercialization, indicating that thetechnology has considerable potential in the marketplace. However, thehigh cost of fuel cells as compared to conventional power generationtechnology deters their widespread use. The cost of fabricating andassembling fuel cells can be significant due to the materials and laborinvolved. Indeed, as much as 85% of a fuel cell's cost can be attributedto manufacturing.

In general, a single cell PEM fuel cell consists of an anode and acathode compartment separated by a thin, ionically conducting membrane.This catalyzed membrane, with or without gas diffusion layers, is oftenreferred to as a membrane electrode assembly (MEA). Energy conversionbegins when the reactants, reductants and oxidants, are supplied to theanode and cathode compartments, respectively, of the PEM fuel cell.Oxidants include pure oxygen, oxygen-containing gases, such as air, andhalogens, such as chlorine. Reductants, also referred to herein as fuel,include hydrogen, natural gas, methane, ethane, propane, butane,formaldehyde, methanol, ethanol, alcohol blends and other hydrogen richorganics. At the anode, the reductant is oxidized to produce protons,which migrate across the membrane to the cathode. At the cathode, theprotons react with the oxidant. The overall electrochemical redox(reduction/oxidation) reaction is spontaneous, and energy is released.Throughout this reaction, the PEM serves to prevent the reductant andoxidant from mixing and to allow ionic transport to occur.

Current state of the art fuel cell designs comprise more than a singlecell, and in fact, generally combine several MEAs, flow fields andseparator plates in a series to form a fuel cell “stack”; therebyproviding higher voltages and the significant power outputs needed formost commercial applications. Flow fields allow for the distribution ofreactants through the fuel cell and are typically separate from theporous electrode layers within the fuel cell. Depending on stackconfiguration, one or more separator plates may be utilized as part ofthe stack design to prevent mixing of the fuel, oxidant and coolingstreams within the fuel cell stack. Such separator plates can alsoprovide structural support to the stack.

Bipolar plates perform the same function as an oxidant flow field, fuelflow field and separator plate in combination and are often used in thedesign of fuel cells as their use can reduce the number of componentsrequired in the functioning fuel cell. These bipolar plates contain anarray of channels formed in the surface of the plate contacting an MEA,which function as the flow fields. The lands conduct current from theelectrodes while the channels between the lands serve to distribute thereactants utilized by the fuel cell and facilitate removal of reactionby-products, such as water. Fuel is distributed from the fuel inlet portto the fuel outlet port, as directed by the channels, on one face of thebipolar plate, while oxidant is distributed from the oxidant inlet portto the oxidant outlet port, as directed by the channels, on the opposingface of the bipolar plate, and the two faces are not connected throughthe plate. The particular design of the bipolar plate flow fieldchannels may be optimized for the operational parameters of the fuelcell stack, such as temperature, power output, gas humidification andflow rate. Ideal bipolar plates for use in fuel cell stacks are thin,lightweight, durable, highly conductive, corrosion resistant structuressuch as carbon/polymer composites or graphite. In the fuel cell stack,each bipolar plate serves to distribute fuel to one MEA of the stackthrough its fuel flow field face while distributing oxidant to a secondMEA through the opposite oxidant flow field face. A thin sheet of porouspaper, cloth or felt, usually made from graphite or carbon, may bepositioned between each of the flow fields and the catalyzed faces ofthe MEA to support the MEA where it confronts grooves in the flow fieldto conduct current to the adjacent lands, and to aid in distributingreactants to the MEA. This thin sheet is normally termed a gas diffusionlayer (GDL) and can be incorporated as part of the MEA.

Of necessity, certain stack components, such as the GDL portion of theMEA, are porous in order to provide for the distribution of reactantsand byproducts into, out of, and within the fuel cell stack. Due to theporosity of elements within the stack, a means to prevent leakage of anyliquid or gases between stack components (or outside of the stack) aswell as to prevent drying out of the various stack elements due toexposure to the environment is also needed. To this end, gaskets orother seals are usually provided between the surfaces of the MEA or PEMand other stack components and on portions of the stack periphery. Thesesealing means, whether composed of elastomeric or adhesive materials,are generally placed upon, fitted, formed or directly applied to theparticular surfaces being sealed. These processes are labor intensiveand not conducive to high volume manufacturing, thereby adding to thehigh cost of fuel cells. Additionally, the variability of theseprocesses results in poor manufacturing yield and poor devicereliability.

Fuel cell stacks may also contain humidification channels within one ormore of the coolant flow fields. These humidification channels provide amechanism to humidify fuel and oxidants at a temperature as close aspossible to the operating temperature of the fuel cell. This helps toprevent dehydration of the PEM as a high temperature differentialbetween the gases entering the fuel cell and the temperature of the PEMcauses water vapor to be transferred from the PEM to the fuel andoxidant streams.

Fuel cell stacks range in design depending upon power output, cooling,and other technical requirements, but may utilize a multitude of MEAs,seals, flow fields and separator plates, in intricate assemblies thatresult in manufacturing difficulties and further increased fuel cellcosts. These multitudes of individual components are typically assembledinto one sole complex unit. The fuel cell stack is formed by compressingthe unit, generally through the use of end plates and bolts, althoughbanding or other methods may be used, such that the gaskets seal and thestack components are held tightly together to maintain electricalcontact there between. These conventional means of applying compressionadd even more components and complexity to the stack and pose additionalsealing requirements.

Various attempts have been made in the fuel cell art to address thesedeficiencies in fuel cell stack assembly design and thereby lowermanufacturing costs. However, most stack assembly designs still requiremanual alignment of the components, active placement of the sealingmeans and/or a multi-step process, each of which presents notabledisadvantages in practice. See, e.g., the processes described in U.S.Pat. No. 6,080,503, to Schmid et al., U.S. Pat. No. 4,397,917, to Chi etal., and U.S. Pat. No. 5,176,966, to Epp et al.

Additionally, in traditional fuel cell cassettes, two types of MEAsdominate; MEAs in which 1) the membrane extends beyond the borders ofthe gas diffusion layers, and 2) gasket materials are formed into theedges of the MEA itself with the membrane and GDLs approximately of thesame size and shape (see, e.g., U.S. Pat. No. 6,423,439 to Ballard). Inthe first type, separate gaskets are used to seal between the membraneedge extending beyond the GDL and the other part of the stack (bipolarplates). In the second type, the gasket of the MEA seals directly to theother parts of the stack. Each of these methods requires compression tomake a seal. These compressive-based seals require that all thecomponents in the stack have high precision such that a uniform load ismaintained. MEA suppliers have become accustomed to supplying the MEAformats above.

Various conventional stacks for use in fuel cells and otherelectrochemical applications utilize an internal manifold design withcompression-based seals. However, there are notable drawbacks associatedwith that architecture. For instance, using a conventionally-sealed,internally manifolded stack there is a significant area that issacrificed in sealing around the MEA and internal manifolds. Onesolution is to locate some or all of the manifolds external to thestack. However, other difficulties are observed in many stacks withexternal manifold designs, such as difficulty sealing between themanifold and the stack. As in traditional stacks, sealing is typicallyaccomplished with gaskets and compression. Unfortunately,gasket/compression based seals have a number of inherent drawbacks,including a sensitivity to thermal cycling, requirements of uniformcompression and associated hardware, high tolerance parts, and delicateassembly requirements.

Still other attempts have been made to improve upon fuel cell design andperformance. For instance, U.S. Pat. No. 4,212,929 describes an improvedsealing method for fuel cell stacks. That patent reports a sealingsystem that utilizes a polymer seal frame clamped between the manifoldand the stack. As described, the seal frame moves with the stack and theleak rate associated with a typical manifold seal is reduced duringcompression. U.S. Pat. No. 5,514,487 and U.S. Pat. No. 5,750,281 bothdescribe an edge manifold assembly that comprises a number of manifoldplates. The plates are mounted on opposite sides of the fuel cell stackand function in such a way to selectively direct the reactant andcoolant streams along the perimeter of the stack. While these designsoffer limited improvements to other conventional assemblies, they aregenerally unsuitable for high-volume manufacture.

Recognizing these and other deficiencies in the art, the Assignee ofthis application has developed a series of innovative methods forsealing manifold ports within the stack or a module thereof, as well asmethods for sealing the stack or module periphery that are less laborintensive and more suitable to high-volume manufacturing processes (seeWorld Publication WO 03/036747). That publication discloses a ‘one-shot’assembly of fuel cell stacks (and other electrochemical devices) inwhich all of the component parts are assembled into a mold withoutgaskets. A resin is introduced into the mold and this resin selectivelypenetrates certain portions of the assembly either by resin transfermolding or injection molding techniques. Upon hardening, that resinseals the components and defines all the manifold channels within thestack. The net effect is to replace the gaskets of the traditional stackwith adhesive based seals, introduced after the assembly of thecomponents.

In another previous patent application, the Assignee of this applicationreported on an innovative fuel cell stack design which assemblestogether individual modules to form a fuel cell stack of requisite poweroutput where each module permanently binds a number of unit cellstogether (see World Publication WO 02/43173).

The assignee also has previously described fuel cells having an MEA inwhich the GDL and membrane were more or less of the same general outlineas each other and of the overall stack profile (see World Publication WO03/092096). A major advantage of that technique is the ability todirectly use a roll-to-roll MEA without having to do any postprocessing. However, a substantial portion of the cross-section of eachMEA is used for sealing the various manifold openings and periphery ofthe stack such that only about 50% of the cell cross section isavailable for the electrochemical reaction.

The assignee also has developed membrane-based electrochemical cells,and more particularly, PEM fuel cell stacks that comprise one or morecomposite MEAs having a molded gasket about the periphery. The gasketportion of the composite MEA has one or more features capable ofregulating the flow of sealant during sealing processes (see WorldPublication 2004/047210).

Despite these advancements over the prior the art, the Assignee of thisapplication has recognized that further improvements can be made to thetechnology. The present invention, as embodied herein, presents suchimprovements.

SUMMARY OF THE INVENTION

The purpose and advantages of the present invention are set forth in andwill become apparent from the description that follows. Additionaladvantages of the invention will be realized and attained by the methodsand systems particularly articulated in the written description andclaims hereof, as well as from the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the invention, as embodied herein, the invention includes a fuel cellstack. The fuel cell stack includes at least one bipolar plate assemblyincluding a first generally planar plate body having a first generallyplanar face. The first face includes an opening defined by the firstplate body for passage of a reactant therethrough, a first reactant flowfield defined thereon, and a first raised surface on the first facesubstantially surrounding the opening. The first raised surface isadapted and configured to mate with a second surface on a face of anadjacent bipolar plate assembly, wherein the first raised surface andsecond surface create a flow obstruction for the encapsulating materialwhen the raised surfaces are mated or positioned in close proximity. Afirst membrane electrode assembly is in operable communication with thefirst reactant flow field. A reactant manifold is in fluid communicationwith the reactant flow field by way of a first fluid flow path. Thereactant manifold is adapted and configured to facilitate transport of areactant through the fuel cell stack. A layer of encapsulating materialis disposed about the separator plate, membrane electrode assembly andreactant manifold. The encapsulating material is substantially preventedfrom flowing into the opening defined by the first plate body by theflow obstruction.

In accordance with a further aspect of the invention, the flowobstruction between the plates is adapted and configured to retainelectrical isolation between the two components and may permit a gasflow therethrough prior to encapsulating material being incorporatedinto the stack. The flow obstruction can be adapted and configured tosubstantially prohibit a gas flow therethrough prior to encapsulatingmaterial being incorporated into the stack. The flow obstruction caninclude an o-ring surrounding the opening.

In accordance with another aspect of the invention, the first raisedsurface includes material that is an electrical insulator, and which maycontact the next plate to effect the flow obstruction for theencapsulating material. The first raised surface can be composed of amaterial different from the first plate body and second plate body. Thefirst raised surface can constitute a monolithic structure incombination with the first plate body. The first raised surface can begenerally ring shaped. The first raised surface can fully surround theopening. It is also possible for the first raised surface to include atleast one interruption therein along its extent.

In accordance with still another aspect of the invention, a secondraised surface is provided substantially surrounding the opening. Thesecond raised surface can substantially surround the first raisedsurface.

The invention also includes a method for making a fuel cell stack. Themethod includes providing a first fuel cell separator plate body havinga first generally planar face. The first plate body defines a firstopening for passage of a reactant therethrough. A first reactant flowfield is defined on the first face, and a first raised surface is on thefirst face substantially surrounding the first opening. The methodfurther includes disposing a first side of a first membrane electrodeassembly in communication with the first reactant flow field. The methodincludes disposing a second fuel cell separator plate body having asecond generally planar face in communication with a second side of themembrane electrode assembly to form a stack. The second face includes asecond opening defined by the second plate body for passage of areactant therethrough. The second face also defines a second reactantflow field thereon. A receiving surface is on the second facesubstantially surrounding the opening. The first raised surface andreceiving surface interfit to define a flow obstruction. The method alsoincludes encapsulating the stack in an encapsulating material. Theencapsulating material is substantially prevented from flowing into theopening defined by the first plate body by the flow obstruction.

The invention further includes a fuel cell stack including a bipolarplate assembly having a first generally planar plate body that includesa first generally planar face defining a first reactant flow field. Theplate body also has a second generally planar face defining a firstopening through the plate body to the first face and a first openchannel in the second planar face extending from the opening toward aperiphery of the plate. The first flow field, first opening and firstopen channel define a first fluid flow path. The fuel cell stack furtherincludes a first membrane electrode assembly having a first face inoperable communication with the first reactant flow field. A reactantmanifold is in fluid communication with the reactant flow field by wayof the first fluid flow path. The reactant manifold is adapted andconfigured to facilitate transport of a reactant through the fuel cellstack. A layer of encapsulating material is disposed about the separatorplate, membrane electrode assembly and reactant manifold. The reactantmanifold is bounded at least in part by the encapsulating material.

In accordance with another aspect of the invention, the bipolar plateassembly further includes a second generally planar plate body having athird generally planar face and a fourth generally planar face inintimate contact with the second face. The third generally planar facecan define a second reactant flow field. The fourth generally planarface can define a second opening through the second plate and a secondopen channel in the fourth planar face extending from the opening towarda periphery of the second plate, wherein the second flow field, secondopening and second open channel further cooperate to define a secondfluid flow path.

A second membrane electrode assembly having a first face in operablecommunication with the second reactant flow field can be included. Thesecond and fourth faces can cooperate to define a coolant flow fieldwithin the separator plate including a channel extending from thecoolant flow field toward the periphery of the plate. The second andforth faces can cooperate to define at least one of: a reactant flowpassage extending from a reactant flow field on an external surface ofthe bipolar plate assembly toward a periphery of the bipolar plateassembly, and a coolant flow passage extending from a coolant flow fieldinside the bipolar plate assembly toward a periphery of the bipolarplate assembly. At least one of the flow passages can terminate at anedge of the bipolar plate assembly at a port, the port having aperimeter defined by the second and fourth faces. A concavity forreceiving a plenum mold insert can be defined by the edge of the plateproximate the port.

The first plate body and second plate body can be an integral structurejoined together at the second planar face and fourth planar face. Thefirst plate body and second plate bodies can be joined by a conductiveadhesive seal. The conductive adhesive seal can be formed from amaterial selected from the group including, for example, a resinmaterial that is chemically compatible with material of the first platebody and second plate body, or an adhesive material, among others.

In accordance with a further aspect of the invention, the second planarface defines a sealant channel therein that substantially surrounds thefirst opening and the first open channel. The sealant channel caninclude first and second ends proximate a periphery of the first platebody. Encapsulating material can be disposed in the sealing channel.Encapsulating material disposed in the sealing channel preferablysubstantially fluidly isolates the reactant channel and the coolantchannel from other fluid sources in the stack.

The invention also includes a method for making a fuel cell stack. Themethod includes providing a bipolar plate assembly comprising a firstgenerally planar plate body having a first generally planar facedefining a first reactant flow field and a second generally planar facedefining a first opening through the plate to the first face. A firstopen channel in the second planar face extends from the opening toward aperiphery of the plate. The first flow field, first opening and firstopen channel define a first fluid flow path. The method also includespositioning a first membrane electrode assembly in operablecommunication with the first reactant flow field and encapsulating theseparator plate and membrane electrode assembly in a layer ofencapsulating material. A reactant manifold is defined at least in partby the encapsulating material. The reactant manifold is adapted andconfigured to facilitate transport of a reactant through the fuel cellstack.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and are intended toprovide further explanation of the invention claimed.

The accompanying drawings, which are incorporated in and constitute partof this specification, are included to illustrate and provide a furtherunderstanding of the method and system of the invention. Together withthe description, the drawings serve to explain the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cut-away perspective view of a portion of a firstrepresentative embodiment of a bipolar plate assembly and stack made inaccordance with the present invention, showing separator plates havingraised surfaces surrounding the openings.

FIG. 2 is a partially cut-away perspective view of a portion of a secondrepresentative embodiment of a bipolar plate assembly and stack made inaccordance with the invention, showing separator plates having raisedsurfaces surrounding the openings in the form of o-rings.

FIG. 3 is a perspective view of the fuel cell stack of FIG. 2, showingmultiple separator plates stacked together.

FIG. 4 is a partial perspective view of a portion of a thirdrepresentative embodiment of a bipolar plate assembly made in accordancewith the present invention, showing raised surfaces surrounding theopenings on the separator plate, wherein one ring-shaped raised surfacesurrounds another ring-shaped raised surface, which surrounds theopening.

FIG. 5 is a partial cut-away perspective view of a fuel cell stack usinga separator plate as depicted in FIG. 4, showing the cross section ofthe raised surfaces defining a tortuous sealant flow path.

FIG. 6 is a partial cut-away perspective view of a portion of the fuelcell stack of FIG. 2, showing an encapsulating material disposed aroundthe manifold portion of the stack.

FIG. 7 is a perspective view of a fourth representative embodiment of astack of bipolar plate assemblies made in accordance with the presentinvention, showing openings into the reactant and coolant flow fields oneither side of a separator plate.

FIG. 8 is a perspective view of a portion of the bipolar plate assemblyof FIG. 7, showing in detail the opening, including an open channel,into the reactant flow field on a separator plate.

FIG. 9 is a perspective view of a portion of the bipolar plate assemblyof FIG. 7, showing the coolant flow field, open channel, and openinginto the coolant flow field, all defined in one surface of the separatorplate.

FIG. 10 is a perspective view of a portion of the fuel cell stack ofFIG. 7, showing the membrane electrode assemblies in place on eitherside of a bipolar plate assembly, as well as plenum molding insertscovering some of the openings in preparation for encapsulating the fuelcell stack in a sealant material.

DETAILED DESCRIPTION

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. The method and corresponding steps of theinvention will be described in conjunction with the detailed descriptionof the system.

The devices and methods presented herein may be used for improving themanufacturability and application of fuel cells. The present inventionis particularly suited for lowering the required tolerances, simplifyingof fuel cell components, such as reactant and coolant manifolds andminimizing labor requirements.

In accordance with a first embodiment of the invention, a fuel cellstack is provided including at least one bipolar plate assembly that hasa first generally planar plate body with a first generally planar face.The first face includes an opening defined by the first plate body forpassage of a reactant therethrough. A first reactant flow field isdefined on the first face, and a first raised surface on the first facesubstantially surrounds the opening. The first raised surface is adaptedand configured to mate with a second surface on a face of an adjacentbipolar plate assembly, wherein the first raised surface and secondsurface create a flow obstruction when the raised surfaces are mated. Afirst membrane electrode assembly is in operable communication with thefirst reactant flow field. A reactant manifold is in fluid communicationwith the reactant flow field by way of a first fluid flow path. Thereactant manifold is adapted and configured to facilitate transport of areactant through the fuel cell stack. A layer of encapsulating materialis disposed about the separator plate, membrane electrode assembly andreactant manifold. The encapsulating material is substantially preventedfrom flowing into the opening defined by the first plate body by theflow obstruction.

For purpose of explanation and illustration, and not limitation, apartial view of an exemplary embodiment of the fuel cell stack inaccordance with the invention is shown in FIG. 1 and is designatedgenerally by reference character 100. Other embodiments of a fuel cellstack in accordance with this embodiment of the invention, or aspectsthereof, are provided in FIGS. 2-6, as will be described.

In accordance with the invention, at least one bipolar plate assembly102 is provided having a first generally planar plate body 104. FIG. 1shows five bipolar plate assemblies 102, including ten individual platebodies 104, stacked together to make a portion of fuel cell stack 100.Each plate body 104 has a first generally planar face 106. An opening108 is defined in each plate body 104. Opening 108 is shown as acircular hole in plate body 104, however, any suitable shape can be usedfor the opening. Openings 108 are designed so that a reactant, such asfuel or an oxidant, can be supplied to the fuel cell stack 100therethrough.

Each plate body 104 has a reactant flow field, such as fuel flow field110 or oxidant flow field 124, defined on one side. The other side mayoptionally define a coolant flow field 126 therein so that when twoplate bodies 104 are arranged back to back, they may combine to enclosethe coolant flow field 126 between them. Two plate bodies 104 arrangedtogether in this manner comprise a bipolar plate assembly 102. As shownin FIG. 1, bipolar plate assembly 102 has a fuel flow field 110 definedon the top face 106, an oxidant flow field 124 defined on the bottomface 114, and a coolant flow field 126 running throughout the middle ofthe bipolar plate assembly 102.

As will be appreciated by those of skill in the art, the term separatorplate, as described herein, refers to a variety of different types ofplates that may be found in a fuel cell stack. For example, separatorplates may include bipolar plates in the middle of a fuel cell stack aswell as terminal plates located proximate end plates of the stack.

As further depicted in FIG. 1, a raised surface 112 is defined on thefirst face 106 of each plate body 104 disposed about opening 108. Asdepicted, raised surface 112 completely surrounds each opening 108,however it is also possible for raised surface 112 to substantiallysurround opening 108 without completely surrounding it, in accordancewith the invention. For example, raised surface 112 may comprise aninterrupted surface or otherwise not completely surround opening 108.Raised surface 112 is preferably designed to mate or align with a secondsurface 114 of an adjacent fuel cell bipolar plate assembly 102, asshown in FIG. 1. When mated, raised surface 112 and second surface 114cooperate to form a flow obstruction. The flow obstruction functions toprevent encapsulating material from freely flowing into opening 108during the encapsulation process, as described below.

A variety of different configurations can be used as flow obstructions.As depicted in FIG. 1, raised surfaces 112 are simply ring shapedfeatures surrounding openings 108. Raised surfaces 112 are preferablymade of a nonconductive material that is different from the conductivematerial of the rest of assembly 102, and are affixed to assembly 102prior to assembly of the stack to reduce part count. In other words,since adjacent bipolar plate assemblies 102 should not be in electricalcontact with one another, the material of raised surfaces 112 shouldprovide electrical insulation between adjacent assemblies 102. By way offurther example, if desired, a non-conductive coating may be used tomaintain isolation. It is also possible to use insulative O-rings inlieu of raised features 112, such as O-rings 212 shown in FIGS. 2, 3,and 6. O-rings 212 can be used create a seal around openings 208 andbetween adjacent separator plates 202, if desired. Preferably, thematerial of raised surfaces 112/212 is compatible with the encapsulationmaterial (described below) to allow for an adhesive seal betweenadjacent bipolar plate assemblies 102/202. Raised surfaces 112 can bemade from a hard compound or a compressible material without departingfrom the spirit and scope of the invention. Moreover, raised surface 112can be a precision-made washer used as a discrete component, or a moreconventional washer precisely located and molded into the plate 104during plate manufacture.

Another example of a flow obstruction in accordance with the inventionis shown in FIGS. 4 and 5. Raised feature 312 is formed monolithicallywith plate 302, which simplifies assembly. Raised feature 312 actuallyincludes two raised ring-shaped features, one surrounding the other.However, it is also possible for one or both of the raised ring-shapedfeatures to have an interruption, as long as feature 312 substantiallysurrounds opening 308. Moreover, it is also possible to use similarfeatures having any suitable shape besides ring-shaped, in accordancewith the invention.

A complementary raised feature 313 is formed opposite to raised feature312 on plate 302. Raised features 312 and 313 of adjacent plates 302cooperate to create a flow obstruction around opening 308. Since it isundesirable for adjacent plates 302 to be in electrical contact,features 312 and 313 of adjacent plates are preferably made fromnonconductive material or have a nonconductive coating disposed thereon.In accordance with another embodiment, the tolerances of features 312,313 may be configured to maintain a gap between the structures toprevent electrical contact. Encapsulating material later incorporatedinto the stack may then pass between features 312, 313. During theencapsulation process (described below), the encapsulating material isrestricted from freely flowing into opening 308 by the combination offeatures 312 and 313.

For purposes of illustration and not limitation, as embodied herein andas depicted in FIG. 1, fuel cell stack 100 is further provided with amembrane electrode assembly 116 (hereinafter “MEA” 116). Stack 100includes an MEA 116 sandwiched between each set of bipolar plateassemblies 102. In a fully assembled cell stack 100, each operationalMEA 116 is in fluid contact with an oxidant flow field 124 on one side,and a fuel flow field 110 on its other side. When in operation, oxidantand fuel flow past opposite sides of MEA 116 to produce electrical poweras known in the art. Those skilled in the art will readily appreciatethat there are numerous suitable materials and configurations for theMEA 116.

In further accordance with the invention, a manifold 118 is provided influid communication with each reactant flow field 110, 124, as well ascoolant flow field 126. Manifold 118 generally includes openings 108,which when stacked generally define a plenum, as best seen in thecross-section portion of FIG. 1. Each fuel cell bipolar plate assembly102 includes one or more passages from plenums 108 to a reactant flowfield 110, 124 or coolant flow field 126. The passage is defined by achannel 122 in second surface 113 of one plate body 104, and the matingface 113 of the adjoined plate body 104 in a separator plate 102.Channel 122 allows fluid to flow from the cylinder defined by the plenumof openings 108 into or out of oxidant flow field 124 (or fuel flowfield 110 on the side opposite that shown in FIG. 1). Similar channels122 communicate between openings 108 and coolant flow field 126. It isalso possible to define channel 122 in each of reciprocally mating faces113, as in channel 222 shown in FIG. 2.

As shown in FIGS. 1-3, each reactant flow field (e.g. 110, 224, 210)flows generally from an opening 108, 208 of a fuel cell bipolar plateassembly 102, 202 to exit at another opening 108, 208 through a pathdesigned to maximize the reactions on MEA 116. However, those skilled inthe art will readily appreciate that a path of any suitable shape can beused in accordance with the invention. In this configuration, manifolds118, 218 allow fuel, oxidant, and coolant to be transported through thefuel cell stack to generate electrical power. Each flow field (fuel,oxidant, and coolant) has a manifold 118, 218 for incoming fluid and amanifold 118, 218 on the opposite side for outgoing fluid, for a totalof six manifolds 118, 218. However, those skilled in the art willreadily appreciate that other configurations/numbers of manifolds can beused without departing from the spirit and scope of the invention.

For purposes of illustration and not limitation, as embodied herein,system 100 includes a layer of encapsulating material disposed about theseparator plate (not shown in FIG. 1). FIG. 6 shows a layer ofencapsulating material 220 encasing manifold 218 of a stack 200. Duringthe process of infusing encapsulating material 220 into the periphery offuel cell stack 200, the flow obstruction (e.g. 112, 212, 312) acts toprevent encapsulating material 220 from freely flowing into opening 108,208, 308. Thereby each plenum defined by a stack of openings (e.g. 108)is kept free from excess encapsulation material 220, which couldotherwise form obstructions within the plenum/manifold to the detrimentof the efficiency of the fuel cell stack 100, 200, 300. The flowobstructions 112, 212, 312 ultimately prevent encapsulating material 220from flowing into channels 122, 222, 322, which could otherwise blockthe channels and prevent proper operation of the fuel cell stack.

To encapsulate the fuel cell stack (e.g., 200), a resin may beintroduced around the periphery, or within injection holes of allassembled components. A vacuum is then pulled through an end plate ofthe stack through each of the manifold holes within the assembly. Thepressure differential introduces resin into the edges of the assemblythereby encapsulating all the edges of the components in the assemblytogether and forming the assembly into a fuel cell stack as described inU.S. Pat. No. 6,946,210, which is incorporated by reference herein inits entirety. Alternately, the pressure differential may be created byapplying pressure to the encapsulant instead of applying vacuum to thefuel cell stack assembly. In addition, the same pressure differentialintroduces the resin into the spaces, if any, defined between a raisedfeature (e.g., 112) on a first plate and the surface of an adjacentseparator plate.

The pressure differential and time required to accomplish the sealingprocess is a function of the materials used in the fuel cell cassetteconstruction. These include, for example, the viscosity and flowcharacteristics of the resin, and the type of gas diffusion layer usedin the MEA. Those skilled in the art will be able to judge theappropriate time and pressure based on these parameters. Thosepracticing the invention may also ascertain the most appropriate timeand pressure by visual inspection during the sealing process with theuse of transparent molds through which the resin progress can be seen inthe topmost layer of the assembly.

A variety of suitable encapsulating materials 220 can be used inaccordance with the invention. Preferably, a resin material that iscompatible with raised features 112, 212, 312 is used to form anadhesive seal therewith. Those skilled in the art will appreciate thatany suitable encapsulating material can be used without departing fromthe spirit and scope of the invention. The resin or sealant used forencapsulation is selected such that it has the required chemical andmechanical properties for the conditions found in an operating fuel cellsystem (oxidative stability, for example). Appropriate resins/sealantsinclude both thermoplastics and thermoset elastomers. Preferredthermoplastics include thermoplastic olefin elastomers, thermoplastic,polyurethanes, plastomers, polypropylene, polyethylene,polytetrafluoroethylene, fluorinated polypropylene and polystyrene.Preferred thermoset elastomers include epoxy resins, urethanes,silicones, fluorosilicones, and vinyl esters.

As further shown in FIG. 6, encapsulation channels 223 are be formed inthe top and bottom surfaces of a plate body 204, which surround opening208 and other portions of manifold 218 to effectively seal against fueland oxidant deviating from the intended flow path in manifold 218 intofields 210, 224. A portion 223 b of channels 223 isolates the edge ofMEA 216 proximate to o-ring 212. As also shown in FIG. 6, O-rings 212may partially or completely block encapsulating material 220 fromflowing into opening 208.

As will be appreciated, it is not necessary for a flow obstruction inaccordance with the invention to completely block encapsulating materialfrom entering the opening. It is sufficient that the flow obstructioninhibit the flow of encapsulating material into the manifold to anextent that leaves the manifold substantially free of obstructions. Forexample, in FIG. 5, a small gap in the form of a tortuous flow path isshown between raised feature 312 and the raised mating feature 313. Itis possible for a fluid (especially a gas) to communicate across thetortuous path of the flow obstruction between features 312 and 313.However, if the viscosity of the encapsulating material is sufficientand/or the material is caused to cure as it approaches opening 108,there will not be a significant flow of encapsulating material throughthe flow obstruction 312, 313.

It is even possible that a small amount of encapsulating material couldfill the tortuous gap and even protrude into the manifold. This wouldcreate a small bump or ridge on the generally cylindrical plenum walldefined by openings 308, however the efficiency of fuel cell stack 300would not be significantly affected thereby as long as encapsulatingmaterial does not substantially obstruct channels 322, for example.Having encapsulating material fill the gap between features 312 and 313can actually be favorable in creating the needed seal inside manifold318, as well as to help electrically insulating adjacent plates 302 fromeach other.

As will be appreciated by those skilled in the art, the encapsulatingmaterial may be hardened, either by cooling of a thermoplastic resin orcuring in the case of a thermoset resin. The encapsulating material canbe cured, partially cured, or thickened to help ensure the effectivenessof the flow obstructing geometry in preventing excessive travel of thematerial into the manifolds as described herein. Several methods can beutilized to accomplish this. For example, a heated gas may be passedthrough the manifold during molding. By way of further example, theseparator plates of the stack may be preheated in the manifold areas,for example, by way of heated inserts which may be removed or left inplace during molding.

With reference to FIGS. 4 and 5, aside from features 312 and 313, fuelcell stack 300 is generally similar to stacks 100 and 200 describedabove, in that fuel cell stack 300 includes separator plates 302, eachof which encloses a coolant flow field 326 at a plate-to plate-interface328. MEA 316 is arranged between adjacent plates 302, thus being incontact with fuel flow field 310 on one side and oxidant flow field 324on the opposite side. Openings 308 communicate with fuel and oxidantflow fields 310, 324 as well as coolant flow field 326, through channels322.

In accordance with another aspect of the invention, a method for makinga fuel cell stack is provided. The method includes providing a bipolarplate assembly including two plate bodies, wherein a first separatorplate body includes a first generally planar face. A first opening isdefined by the first plate body for passage of a reactant therethrough.The first face has a first reactant flow field defined thereon. A firstraised surface is disposed or formed on the first face, substantiallysurrounding the first opening. The method further includes disposing afirst side of a first MEA in communication with the first reactant flowfield. The method also includes disposing a second fuel cell separatorplate body having a second generally planar face in communication with asecond side of the MEA to form a stack. The second face includes asecond opening defined by the second plate body for passage of areactant therethrough. A second reactant flow field is defined on thesecond face. A receiving surface is disposed or formed on the secondface substantially surrounding the opening. The first raised surface andreceiving surface interfit to define a flow obstruction. The method alsoincludes encapsulating the stack about its periphery using anencapsulating material, wherein the encapsulating material issubstantially prevented from flowing into the opening defined by thefirst plate body by the flow obstruction.

For purposes of illustration and not limitation, as embodied herein andas depicted in FIGS. 1-6, a first fuel cell separator plate body of afirst bipolar plate assembly having a generally planar face is provided(e.g. plate body 104). A first opening (e.g. 108, 208, 308) is definedin the first plate body. A reactant flow field (e.g. fuel flow field110, 210, 310) is defined on the first face of the plate body. Also, afirst raised surface (e.g. 112, 212, 312) is disposed or formed on thefirst face. The first raised surface substantially surrounds the firstopening. The flow field, opening, and raised surface can all be formedin the provided plate body by processes well known in the art.

In further accordance with the invention, the method includes theadditional step of disposing a first side of a first MEA (e.g. 116, 216,316) in communication with the first reactant flow field, as describedabove. Suitable MEA materials and configurations will be readilyapparent to those skilled in the art.

In further accordance with the method of the invention, the method alsoincludes disposing a second fuel cell separator plate body (e.g. 104)having a second generally planar face in communication with a secondside of the MEA. The second plate body defines a second opening (e.g.108, 208, 308) for passage of a reactant therethrough. A second reactantflow field (e.g. 124, 224, 324) is defined on the second face. Areceiving surface is disposed or formed on the second face substantiallysurrounding the opening. The first raised surface and receiving surfaceinterfit to define a flow obstruction, as described above in conjunctionwith stacks 100, 200, and 300.

The method in accordance with the invention also includes encapsulatingthe stack about its periphery using an encapsulating material (e.g.220), as shown for example in FIG. 6. By way of example and notlimitation, the stack (e.g. 100, 200, 300) can be placed in a mold andresin can be infused into the mold by known techniques to encapsulatethe stack. The encapsulating material is substantially prevented fromflowing into the opening defined by the first plate body by the flowobstruction, as described above with reference to stacks 100, 200, and300. It is possible, for example, to move encapsulating material in toseal the flow obstruction by applying a vacuum to the plenum formed bythe openings (e.g. 108) and/or by applying pressure to the resin. Aswill be appreciated, the method in accordance with the invention caninclude any other suitable step for making the fuel cell stacksdescribed above.

The method and fuel cell stacks described above in conjunction withFIGS. 1-6 provide several advantages over the state of the art in fuelcell manufacturing. Since the manifold features are provided within theseparator plates, there is no need for manufacturing complex externalmanifolds. Moreover, due to the use of encapsulating material, whichseals the manifold and encases the stack, tolerances (e.g. surfacefinish, geometric tolerances, allowable draft angle, allowable edgeradii, etc.) on the individual plates can be relaxed somewhat. Also,less post-machining is required. Therefore, manufacturing fuel cellstacks in accordance with the present invention is a simpler and lessexpensive alternative to conventional stack manufacturing methods.

In further accordance with the invention, a fuel cell stack is providedincluding a bipolar plate assembly having a first generally planar fuelcell separator plate body. The first generally planar plate body has afirst generally planar face that defines a first reactant flow field. Asecond generally planar face defines a first opening through the platebody to the first face and a first open channel in the second planarface extending from the opening toward a periphery of the plate. Thefirst flow field, first opening, and first open channel define a firstfluid flow path. The fuel cell stack further includes a first MEA havinga first face in operable communication with the first reactant flowfield. A reactant manifold is in fluid communication with the reactantflow field by way of the first fluid flow path. The reactant manifold isadapted and configured to facilitate transport of a reactant through thefuel cell stack. A layer of encapsulating material is disposed about theseparator plate, MEA, and reactant manifold. The reactant manifold isbounded at least in part by the encapsulating material.

For purpose of explanation and illustration, and not limitation, viewsof an exemplary embodiment of the fuel cell stack made in accordancewith this aspect of the invention are depicted in FIGS. 7-10.

In accordance with the invention, and with reference now to FIG. 7, abipolar plate assembly 402 is provided including a first generallyplanar plate body 404 a. A second generally planer plate body 404 b isalso shown in FIG. 4. This second plate body may be integrally joinedback to back with plate body 404 a. Plate bodies 404 a, 404 b arepreferably joined together with a conductive, adhesive seal formedtherebetween. Appropriate sealing materials include resin materials thatare chemically compatible with the materials of plate bodies 404 a,b,and other suitable adhesive materials known in the art. Such materialsmay also be used to seal together the plate bodies of the embodiment ofFIGS. 1-6. Each plate body 404 has a first generally planar facedefining a first reactant flow field 410, which is similar to the flowfields (e.g. 110) described above with reference to fuel cell stacks100, 200, and 300.

In further accordance with the invention, and as shown in FIG. 8, eachplate body 404 includes a second generally planar face that defines afirst opening 409 through the plate body 404. Opening 409 communicatesfrom the second face to the flow field 410 defined in the first face. Afirst open channel 422 extends from opening 409 to the edge of platebody 404. Thus, there is a flow path starting from the edge of platebody 404, through first channel 422 and opening 409, and into flow field410.

With reference now to FIG. 9, each plate body 409 has coolant flow field426 defined on the face opposite of flow field 410. When two platebodies 404 are joined, as shown in FIG. 10, coolant channels are formedby the joining of the two coolant flow fields 426. Coolant flow fields,and use of coolant in general, are optional. The invention can besuitably practiced without coolant fields, however, those skilled in theart will readily appreciate the advantages of controlling temperaturesin fuel cell stack 400 by use of coolant channels. Various bondingmethods may be selectively employed to join plate bodies 404, as long asthe bonding agent and location also creates a sealed interface betweenthe various areas of the plate in the plate-to-plate region.Alternately, the design allows for no plate bonding to be used, sinceall of the necessary seals may be created at the encapsulation step.

With continuing reference to FIG. 9, channels 422 can be seen. Thechannels 422 in opposite corners of plate body 404 as shown in FIG. 9serve for ingress and egress of a reactant fluid to and from reactantflow field 410, shown in FIGS. 7-8. When two plate bodies 404 are matedto form a bipolar plate assembly 402, corner channels 422 in each plateare mated with flat channel surfaces 421 in the other plate. The channel422 in the center (communicating with the coolant flow fields 426) ofone plate body 404 mate with center channels 422 in the opposite platebody 404. Those skilled the art will readily appreciate that the channelconfiguration used in the center channels 422, namely wherein channels422 are matched with each other across mated plates 404 rather thanmatched with flat surfaces 421, will also work in the corner channels(see e.g. channel 222 in FIG. 2), and vice versa, without departing fromthe spirit and scope of the invention.

With reference now to FIGS. 7 and 10, MEA 416 is disposed on each ofplate bodies 404 a and 404 b. Each MEA 116 has a face that is inoperable, fluid communication with a reactant flow field 410, asdescribed above with reference to fuel cell stacks 100, 200, and 300.

For purposes of illustration and not limitation, as embodied herein andwith reference to FIGS. 6-10, fuel cell stack 400 includes a reactantmanifold in fluid communication with reactant flow field 410 through theopening 409 and channel 422. A layer of encapsulating material (forreference, see FIG. 6) is disposed about the separator plate, MEA, andreactant manifold. The reactant manifold is thus bounded at least inpart by the encapsulating material.

The reactant manifold is designed to conduct fuels, oxidants, andcoolants through fuel cell stack 400, as described above. The manifoldcan be made using features defined in the separator plates, such asopenings 108, 208, and 308, etc., as described above. As depicted inFIG. 10, however, fuel cell stack 400 has a manifold that is formedlargely of an encapsulating material molded around stack 400. Plenummolding inserts 430 are shown in FIG. 10 partially embraced byconcavities in the edges of separator plate 402. Inserts 430 therebyblock the openings into channels 422 in separator plate 402 for purposesof molding. After stack 400 is encased in encapsulating material, andafter plenum molding inserts 430 are removed, a manifold will have beenformed, as described in detail in co-pending U.S. patent applicationSer. Nos. 11/784,941 and 11/786,082, each of which is incorporated byreference herein in its entirety.

Encapsulation channels 423 are shown surrounding corner channels 422 inFIG. 9. The ends of each encapsulation channel 423 reach edges of platebody 404. Channels 423 can be infused during the main molding process,or can be molded separately, to help seal reactant flow fields 410 fromcoolant flow fields 426 as described above. Channels 423 surroundopenings 409, however, it is also possible to practice the inventionwith channels 423 that only partially surround openings 409, or withoutchannels 423 altogether, as long as the sealing function betweenopenings 409 and flow field 426 is retained.

Another advantage of fuel cell stack 400 is that plate bodies 404 canall be substantially identical. Moreover, side-holes do not need to bedrilled into the plates, because they are formed by the cooperation ofchannels/surfaces defined in the individual mated plate bodies, whilecooling layers are provided at every cell. As with cell stacks 100, 200,and 300, the use of encapsulating material to seal and/or form part ofthe manifold allows for relaxed tolerances in plate bodies 404.

In accordance with another aspect of the invention, a method for makinga fuel cell stack is provided. The method includes providing a bipolarplate assembly that has a first generally planar plate body having afirst generally planar face defining a first reactant flow field. Asecond generally planar face defines a first opening through the plateto the first face and a first open channel in the second planar faceextending from the opening toward a periphery of the plate. The firstflow field, first opening and first open channel define a first fluidflow path. The method includes positioning a first MEA in operablecommunication with the first reactant flow field. The method furtherincludes encapsulating the separator plate and MEA in a layer ofencapsulating material. A reactant manifold is defined at least in partby the encapsulating material. The reactant manifold is adapted andconfigured to facilitate transport of a reactant through the fuel cellstack.

For purposes of illustration and not limitation, as embodied herein andas depicted in FIGS. 1-10, a first fuel cell bipolar plate assembly(e.g. 102, 202, 302, 402) is provided. The bipolar plate assemblyincludes a first generally planar plate body (e.g. 104, 204, 304, 404),which includes a first generally planar face (e.g. 106) defining a firstreactant flow field (e.g. 110, 210, 310, 410). A second generally planarface (e.g. 113) defines a first opening (e.g. 108, 208, 308, and the netshape created by part 430 during the molding process) through the plateto the first face and a first open channel (e.g. 122, 222, 322, 422) inthe second planar face extending from the opening toward a periphery ofthe plate. The first flow field, first opening, and first open channeldefine a first fluid flow path.

In further accordance with the method of the invention, an MEA (e.g.116, 216, 316, 416) is positioned in operable communication with thefirst reactant flow field. With the MEA in place, the step ofencapsulating the separator plate and MEA in a layer of encapsulatingmaterial (e.g. 220) is performed. At least a part of a reactant manifold(e.g. 118, 218) is defined by the encapsulating material. The manifoldcan be of the type described above with reference to stack 400 shown inFIG. 10, in which plenum inserts are used to keep encapsulating materialfrom entering the channels during molding. It is also possible for themanifold to be of the type described above with reference to stacks 100,200, and 300, in which the plates include most of the manifold featuresbefore being encased in encapsulating materials.

The methods and systems of the present invention, as described above andshown in the drawings, provide for a fuel cell stack with superiorproperties including ease of manufacture. Each and every documentreferred to herein is incorporated by reference in its entirety. It willbe apparent to those skilled in the art that various modifications andvariations can be made in the device and method of the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention include modifications and variationsthat are within the scope of the appended claims and their equivalents.

1. A fuel cell stack comprising: a) at least one bipolar plate assemblyincluding a first generally planar plate body having a first generallyplanar face, the first face including: i) an opening defined by thefirst plate body for passage of a reactant therethrough; ii) a firstreactant flow field defined thereon; and iii) a first raised surface onthe first face substantially surrounding the opening, the first raisedsurface being adapted and configured to mate with a second surface on aface of an adjacent bipolar plate assembly, wherein the first raisedsurface and second surface create a flow obstruction when the raisedsurfaces are mated; b) a first membrane electrode assembly in operablecommunication with the first reactant flow field; c) a reactant manifoldin fluid communication with the reactant flow field by way of a firstfluid flow path, the reactant manifold being adapted and configured tofacilitate transport of a reactant through the fuel cell stack; and d) alayer of encapsulating material disposed about the separator plate,membrane electrode assembly and reactant manifold, wherein theencapsulating material is substantially prevented from flowing into theopening defined by the first plate body by the flow obstruction.
 2. Thefuel cell stack of claim 1, wherein the flow obstruction is adapted andconfigured to permit a gas flow therethrough prior to encapsulatingmaterial being incorporated into the stack.
 3. The fuel cell stack ofclaim 1, wherein the flow obstruction is adapted and configured tosubstantially prohibit a gas flow therethrough prior to encapsulatingmaterial being incorporated into the stack.
 4. The fuel cell stack ofclaim 1, wherein the first raised surface includes material that is anelectrical insulator.
 5. The fuel cell stack of claim 1, wherein thefirst raised surface is composed of a material different from the firstplate body and second plate body.
 6. The fuel cell stack of claim 1,wherein the flow obstruction includes an o-ring surrounding the opening.7. The fuel cell stack of claim 1, wherein the first raised surfaceconstitutes a monolithic structure in combination with the first platebody.
 8. The fuel cell stack of claim 1, wherein the first raisedsurface is generally ring shaped.
 9. The fuel cell stack of claim 1,wherein the first raised surface fully surrounds the opening.
 10. Thefuel cell stack of claim 1, wherein the first raised surface includes atleast one interruption therein along its extent.
 11. The fuel cell stackof claim 1, further comprising a second raised surface substantiallysurrounding the opening.
 12. The fuel cell stack of claim 11, whereinthe second raised surface substantially surrounds the first raisedsurface.
 13. A method of making a fuel cell stack comprising: a)providing a first bipolar plate assembly body having a first generallyplanar face, the first face including: i) a first opening defined by thefirst plate body for passage of a reactant therethrough; ii) a firstreactant flow field defined on the first face; and iii) a first raisedsurface on the first face substantially surrounding the first opening;b) disposing a first side of a first membrane electrode assembly incommunication with the first reactant flow field; c) disposing a secondbipolar plate assembly having a second generally planar face incommunication with a second side of the membrane electrode assembly toform a stack, the second face including: i) a second opening defined bythe second plate body for passage of a reactant therethrough; ii) asecond reactant flow field defined on the second face; and iii) areceiving surface on the second face substantially surrounding theopening, wherein the first raised surface and receiving surface interfitto define a flow obstruction; and d) encapsulating the stack in anencapsulating material, wherein the encapsulating material issubstantially prevented from flowing into the opening defined by thefirst plate body by the flow obstruction.
 14. The method of claim 13,wherein the flow obstruction is adapted and configured to permit a gasflow therethrough prior to encapsulating material being incorporatedinto the stack.
 15. The method of claim 13, wherein the flow obstructionis adapted and configured to substantially prohibit a gas flowtherethrough prior to encapsulating material being incorporated into thestack.
 16. The method of claim 13, wherein the first raised surfaceincludes material that is an electrical insulator.
 17. The method ofclaim 13, wherein the first raised surface is composed of a materialdifferent from the first plate body and second plate body.
 18. Themethod of claim 13, wherein the flow obstruction includes an o-ringsurrounding the opening.
 19. The method of claim 13, wherein the firstraised surface constitutes a monolithic structure in combination withthe first plate body.
 20. The method of claim 13, wherein the firstraised surface is generally ring shaped.